- Introduction
Passive optofluidic sorting offers a precise and label-free approach for directing and stabilizing nanoparticles of various sizes along controlled trajectories by leveraging the interplay between optical and hydrodynamic forces. In this work, we analyze a device designed to separate nanoparticles, aiming to reach the exosomal size range (typically 150-200 nm), a challenging task when using passive techniques.
2. Methods and results
The system consists of three silicon waveguides embedded in a CYTOP layer and arranged in a three-step directional coupler (power splitting ratio of 4:1) configuration, integrated with a microchannel through which water flows as the carrier fluid, transporting the suspended nanoparticles. Simulations were performed using the three-dimensional Finite Element Method approach, incorporating optical forces, creeping flow dynamics, and particle tracing analysis. Starting from the optical forces acting on nanoparticles of different sizes, we designed the microfluidic channel such that the drag forces counterbalance the optical ones, stabilizing particle positions. By integrating both effects and tracking the particle dynamics within the microchannel, we demonstrate controlled particle deflection and size-selective trajectory steering. Nanospheres with diameters of 500 nm, 600 nm, and 700 nm are effectively separated due to the action of transverse trapping force of 46.46 pN/W, 52,76 pN/W, and 58.26 pN/W, respectively, with input power of 20 mW.
3. Conclusions
This configuration optimizes the photonic and microfluidic integration to enhance particle discrimination resolution, showing great potential for biomedical use, especially in early cancer diagnostics, where sorting exosome-sized particles is crucial.
